Winter sucks!
Anyways, if I end up removing the snorkel or putting holes in the airbox cover, do I HAVE to rejet. I mean, is it 100% neccesarry?

Not in my experience. Half Pint is my 2006 XT225. Her power train is unviolated right down to the brass plug. At 28,000 miles and counting we lived at -200' (Death Valley) the past two months. To date the highest elevation we've ridden is +10,000' which she pulled in upper gears until road/weather conditions slowed us down. (All averaging 90 +/- 5 mpg BTW.)